<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Daytime.4 - A synchronous UDP daytime client</title>
    <link rel="stylesheet" href="../../boostbook.css" type="text/css">
    <meta name="generator" content="DocBook XSL Stylesheets V1.75.2">
    <link rel="home" href="../../index.html" title="Asio">
    <link rel="up" href="../tutorial.html" title="Tutorial">
    <link rel="prev" href="tutdaytime3/src.html" title="Source listing for Daytime.3">
    <link rel="next" href="tutdaytime4/src.html" title="Source listing for Daytime.4">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%">
    <tr>
        <td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../asio.png"></td>
    </tr>
</table>
<hr>
<div class="spirit-nav">
    <a accesskey="p" href="tutdaytime3/src.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u"
                                                                                             href="../tutorial.html"><img
        src="../../up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../home.png"
                                                                                      alt="Home"></a><a accesskey="n"
                                                                                                        href="tutdaytime4/src.html"><img
        src="../../next.png" alt="Next"></a>
</div>
<div class="section">
    <div class="titlepage">
        <div>
            <div><h3 class="title">
                <a name="asio.tutorial.tutdaytime4"></a><a class="link" href="tutdaytime4.html"
                                                           title="Daytime.4 - A synchronous UDP daytime client">Daytime.4
                - A synchronous
                UDP daytime client</a>
            </h3></div>
        </div>
    </div>
    <p>
        This tutorial program shows how to use asio to implement a client application
        with UDP.
    </p>
    <pre class="programlisting"><span class="special">#</span><span class="identifier">include</span> <span
            class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="special">#</span><span class="identifier">include</span> <span class="special">&lt;</span><span
                class="identifier">boost</span><span class="special">/</span><span class="identifier">array</span><span
                class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="special">#</span><span class="identifier">include</span> <span class="special">&lt;</span><span
                class="identifier">asio</span><span class="special">.</span><span class="identifier">hpp</span><span
                class="special">&gt;</span>

<span class="keyword">using</span> <span class="identifier">asio</span><span class="special">::</span><span
                class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span
                class="special">;</span>
</pre>
    <p>
        The start of the application is essentially the same as for the TCP daytime
        client.
    </p>
    <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span
            class="special">(</span><span class="keyword">int</span> <span class="identifier">argc</span><span
            class="special">,</span> <span class="keyword">char</span><span class="special">*</span> <span
            class="identifier">argv</span><span class="special">[])</span>
<span class="special">{</span>
  <span class="keyword">try</span>
  <span class="special">{</span>
    <span class="keyword">if</span> <span class="special">(</span><span class="identifier">argc</span> <span
                class="special">!=</span> <span class="number">2</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span
                class="special">&lt;&lt;</span> <span class="string">"Usage: client &lt;host&gt;"</span> <span
                class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span
                class="identifier">endl</span><span class="special">;</span>
      <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
    <span class="special">}</span>

    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span> <span
                class="identifier">io_context</span><span class="special">;</span>
</pre>
    <p>
        We use an <a class="link" href="../reference/ip__udp/resolver.html"
                     title="ip::udp::resolver">ip::udp::resolver</a>
        object to find the correct remote endpoint to use based on the host and service
        names. The query is restricted to return only IPv4 endpoints by the <a class="link"
                                                                               href="../reference/ip__udp/v4.html"
                                                                               title="ip::udp::v4">ip::udp::v4()</a>
        argument.
    </p>
    <pre class="programlisting">    <span class="identifier">udp</span><span class="special">::</span><span
            class="identifier">resolver</span> <span class="identifier">resolver</span><span
            class="special">(</span><span class="identifier">io_context</span><span class="special">);</span>
    <span class="identifier">udp</span><span class="special">::</span><span class="identifier">endpoint</span> <span
                class="identifier">receiver_endpoint</span> <span class="special">=</span>
      <span class="special">*</span><span class="identifier">resolver</span><span class="special">.</span><span
                class="identifier">resolve</span><span class="special">(</span><span class="identifier">udp</span><span
                class="special">::</span><span class="identifier">v4</span><span class="special">(),</span> <span
                class="identifier">argv</span><span class="special">[</span><span class="number">1</span><span
                class="special">],</span> <span class="string">"daytime"</span><span class="special">).</span><span
                class="identifier">begin</span><span class="special">();</span>
</pre>
    <p>
        The <a class="link" href="../reference/ip__basic_resolver/resolve.html" title="ip::basic_resolver::resolve">ip::udp::resolver::resolve()</a>
        function is guaranteed to return at least one endpoint in the list if it
        does not fail. This means it is safe to dereference the return value directly.
    </p>
    <p>
        Since UDP is datagram-oriented, we will not be using a stream socket. Create
        an <a class="link" href="../reference/ip__udp/socket.html" title="ip::udp::socket">ip::udp::socket</a> and
        initiate contact with the remote endpoint.
    </p>
    <pre class="programlisting">    <span class="identifier">udp</span><span class="special">::</span><span
            class="identifier">socket</span> <span class="identifier">socket</span><span class="special">(</span><span
            class="identifier">io_context</span><span class="special">);</span>
    <span class="identifier">socket</span><span class="special">.</span><span class="identifier">open</span><span
                class="special">(</span><span class="identifier">udp</span><span class="special">::</span><span
                class="identifier">v4</span><span class="special">());</span>

    <span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span><span
                class="special">&lt;</span><span class="keyword">char</span><span class="special">,</span> <span
                class="number">1</span><span class="special">&gt;</span> <span class="identifier">send_buf</span>  <span
                class="special">=</span> <span class="special">{{</span> <span class="number">0</span> <span
                class="special">}};</span>
    <span class="identifier">socket</span><span class="special">.</span><span class="identifier">send_to</span><span
                class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span
                class="identifier">buffer</span><span class="special">(</span><span
                class="identifier">send_buf</span><span class="special">),</span> <span class="identifier">receiver_endpoint</span><span
                class="special">);</span>
</pre>
    <p>
        Now we need to be ready to accept whatever the server sends back to us. The
        endpoint on our side that receives the server's response will be initialised
        by <a class="link" href="../reference/basic_datagram_socket/receive_from.html"
              title="basic_datagram_socket::receive_from">ip::udp::socket::receive_from()</a>.
    </p>
    <pre class="programlisting">    <span class="identifier">boost</span><span class="special">::</span><span
            class="identifier">array</span><span class="special">&lt;</span><span class="keyword">char</span><span
            class="special">,</span> <span class="number">128</span><span class="special">&gt;</span> <span
            class="identifier">recv_buf</span><span class="special">;</span>
    <span class="identifier">udp</span><span class="special">::</span><span class="identifier">endpoint</span> <span
                class="identifier">sender_endpoint</span><span class="special">;</span>
    <span class="identifier">size_t</span> <span class="identifier">len</span> <span class="special">=</span> <span
                class="identifier">socket</span><span class="special">.</span><span
                class="identifier">receive_from</span><span class="special">(</span>
        <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span
                class="special">(</span><span class="identifier">recv_buf</span><span class="special">),</span> <span
                class="identifier">sender_endpoint</span><span class="special">);</span>

    <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span><span
                class="special">.</span><span class="identifier">write</span><span class="special">(</span><span
                class="identifier">recv_buf</span><span class="special">.</span><span
                class="identifier">data</span><span class="special">(),</span> <span class="identifier">len</span><span
                class="special">);</span>
  <span class="special">}</span>
</pre>
    <p>
        Finally, handle any exceptions that may have been thrown.
    </p>
    <pre class="programlisting">  <span class="keyword">catch</span> <span class="special">(</span><span
            class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span
            class="special">&amp;</span> <span class="identifier">e</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span
                class="special">&lt;&lt;</span> <span class="identifier">e</span><span class="special">.</span><span
                class="identifier">what</span><span class="special">()</span> <span
                class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span
                class="identifier">endl</span><span class="special">;</span>
  <span class="special">}</span>

  <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
    <p>
        See the <a class="link" href="tutdaytime4/src.html" title="Source listing for Daytime.4">full source listing</a>
    </p>
    <p>
        Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a>
    </p>
    <p>
        Previous: <a class="link" href="tutdaytime3.html" title="Daytime.3 - An asynchronous TCP daytime server">Daytime.3
        - An asynchronous
        TCP daytime server</a>
    </p>
    <p>
        Next: <a class="link" href="tutdaytime5.html" title="Daytime.5 - A synchronous UDP daytime server">Daytime.5 - A
        synchronous
        UDP daytime server</a>
    </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%">
    <tr>
        <td align="left"></td>
        <td align="right">
            <div class="copyright-footer">Copyright © 2003-2022 Christopher M. Kohlhoff<p>
                Distributed under the Boost Software License, Version 1.0. (See accompanying
                file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
            </p>
            </div>
        </td>
    </tr>
</table>
<hr>
<div class="spirit-nav">
    <a accesskey="p" href="tutdaytime3/src.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u"
                                                                                             href="../tutorial.html"><img
        src="../../up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../home.png"
                                                                                      alt="Home"></a><a accesskey="n"
                                                                                                        href="tutdaytime4/src.html"><img
        src="../../next.png" alt="Next"></a>
</div>
</body>
</html>
